1 Lucky Texan

not certain about the following for an '07 but.... when the alarm is sounding, cycle the key from off-to on 3 times quickly. then, you should try to re-assign the fobs to the car. Pretty sure on an '07 there's still a procedure to do that. check your manual or maybe over at www.cars101.com

spray them with PB blaster or, brush them with 50:50 ATF/Acetone shaken-mixed-up. Maybe you need some Irwing ez-off type tools if you're saying the nuts are rounded-off ??? https://www.lowes.com/pd/irwin-bolt-grip-5-pack-bolt-extractor-set/1000363541?cm_mmc=shp-_-c-_-prd-_-tah-_-google-_-lia-_-151-_-specialtyhandtools-_-1000363541-_-0&kpid&store_code=2546&k_clickID=go_625706834_34613852470_111132719110_aud-305162224742:pla-260326515041_c_9027195&gclid=CjwKCAiA4t_iBRApEiwAn-vt-5gEdMg02GmRcrnuDwdsi5rhEtzqTkHxoMGTqNrwVBnwE7oLeLeY-BoC6oUQAvD_BwE good luck

at 225K miles, why not a used engine? maybe JDM ?

timing belt tenisoner uh, 'knock-mimic' wouldn't change with a change in oil viscosity. And, rod knock almost invariable gets worse/more aggressive-sounding with rpm increase. Most folks say piston slap reduces as engine temp gets to operating temp. It also would respond to a oil vis. change I'd think. Piston slap and rod knock would probably both be found in a used oil analysis from Blackstone labs as they increase metals. Tensiioner knock kinda comes and goes and can even quiet-down at some rpms. there is a youtube video showing tensioner knock.

(edited out bad info) fans may be coming on when the ECU detects open circuit ???

find a local independent mech. that is Subaru friendly - you may need one anyway for a prepurchase inspection. Ask if he has any Subaru-owning customers that might be trading-up soon. but, the older a car is, the less important the brand and the more important the past care and present condition.

any difference with cold vs warm engine? any smell of fuel under the hood? You can check the charging voltage with a voltmeter. rev a little and it should be around 14 - 14.4 or so I think (others will correct me if I'm wrong) voltage while cranking should probably be about 10 or so. nothing wrong with having the battery and maybe the alt checked at the parts store - but MANY people find typical parts store rebuilt alternators to be very poor risk. If your alt is really bad, a used one from car-part.com or having your original rebuilt locally is a better wat to go. Or check into DBW or Maniac for an alternator. An 08 may have the Mitsubishi planetary starter - they can be noisy/slow to release sometimes but, I haven't read any complaints of 'dragging'. used car lot may be installing very cheap batteries to get cars out-the-door.

that test only works in neutral I 'think' - that's how it works on our Outback, so, was the driveshaft also turning? you might dig around at www.cars101.com to determine if that year-model had rear LSD.

don't drive it if it's overheating - headgaskets might be compromised. Check coolant level IN THE RADIATOR until this is resolved. don't rely on the overflow to accurately reflect total coolant volume. could be a bad hose or hose connection - or leaking crimp or cracked plastic on the rad. but sounds to me like you have a good sense of how to proceed. hoping it's an easy fix.

I admit to being ignorant of this type transmission, but, running the odd size pair on one SIDE , or opposite corners, might avoid binding if the rear and front diffs are 'open'. best is 4 IDENTICAL tires; brand, size and model. Also, near each other in wear. Subaru has always claimed the rolling circumference needs to be within 1/4" .

on an '06, the rear sensor may be more than just a cat conv 'nanny'. best to be prepared for a new cat but, catching up on any lapsed maintenance and examining for exhaust leaks, vacuum leaks and anything else that may throw-off the a:f ratio is important.

clear the codes and see which ones come back after a failed start. slipped timing does seem like a possibility.

you could try some ohmmeter measurements with the hatch closed, open, ...maybe have a helper push,pull,wiggle the boot.

could be a shorted wire in the 'boot' from the body to the hatch.

diff bushings fail and could transmit a lot of noise

is 06 Forry DBW ?

I haven't done it though my '03 has very slight clicking at the inner tierod (that ball-and-socket). we can get aftermarket or OEM of course, and parts stores loan the tools. I HAVE read of people using pipe wrenches to swap. but, you need to first fine where the problem is - it seems too loud to be an inner tire rod. I have read of adjustments to the rack itself, dunno much about that. Seems most people just get used racks from junkyards. just depends of the source of the problem.

grab different parts and try to move them - pin-dowm where the movement is;

yikes

yeah - check all fluid levels and look for a split CV boot. Probably a good idea to confirm cam/crank timing. If it slips a tooth it might still start and run with reduced power. what the smoke smelled like could be a clue - VERY stinky is likely CV grease, sweet-ish toasted marshmallow smell is coolant. Rubber....hmmm, could be a seized timing belt idler ? Or, maybe a delaminated crank pulley....? hard to say without further data

scan for trouble codes . if knock sensors go bad they can cause loss of power without always throwing a check engine light.

hmmm....seems almost like steering rack bushings issue - seems too loud to be inner tierods...... if you put the front up on jack stands, can you duplicate the problem shifting the wheels front to back (9 o'clock to 3 o'clock) ? Or, grab the tierods and push-pull? (not a bad idea to try lift-rocking them too, bad wheel bearing will allow movement in the 6 o'clock-12 o'clock , should be solid) compare left side to right side. seems too loud to be the little u-joint on the steering shaft but, they can go bad or begin binding.

I haven't looked for axle numbers but, you could try www.opposedforces.com

yeah, the invention of the lock-up TC was probably the last blow to the MT.

weakest link is gonna break. new Subaru axles are very pricey but, maybe a good idea for your usage. a local tuner often uses FEQ heavy-duty axles from World Pac (??? dunno if you can get those) no question about the above advice, many of us regrease and reboot used OEM (green inner cups - made by NTN)