forester2002s

On most models, all the warning lamps are tested during start-up: - turn the key to the ON position (just prior to turning the key to START the engine); the display should show all warning lamps illuminated, including the check-engine-lamp; this verifies which warning lamps actually work (or not).

Seized rear-diff?

Recently filled-up with (bad) gas?

10%? That seems way too large a difference.

Could be a CV-joint, especially if the vibration seems to be from one wheel only. And more likely a front CV-joint, as you say that the steering wheel shakes. Or could be the universal-joint and/or support-bearing on the rear drive-shaft.

If it has a cracked head, the coolant likely leaks, and it may have a history of overheating. Beware!

Does the car still have the original engine?

Aside from the same-diameter situation, I would expect that (or at least not-be-surprised if) on-highway driving performance would be affected. I'm thinking that different manufacturers would have their own preferred tread-design and configuration of internal metal/fabric plies. Just how any of this might affect emergency swerving or braking, or cold-weather grip, is an open question. Personally, I wouldn't risk it.

Could it be a problem with the wiring between the speed sensor and the cluster?

A reminder: Take photographs of the old timing belt before removal, including timing marks. It will make installing the new belt easier.

For my 2017 Forester, I have received these 2 documents from Subaru Canada: - Warranty Enhancement Program CVT for 2016-2017 - 10 years or 160,000km - Warranty Enhancement for CVT Park Range Switch - 8 years (2013-18 various models, no mention of Ascent)

Changed the belt and the noise went away? Maybe it's not the belt, but the tension that changed? That squeak sounds like a bearing noise to me.

Sometimes a bad ground can cause electrical mayhem. May or may not be related to your problems.

The problem might not be with the sensor itself, but with the wiring/plugs that connect to the sensor.

Have you checked for any DTCs (Diagnostic Trouble Codes), using an OBDII scanner?