1998 Outback Sport, engine makes clicking noise under load

[psychocandy]

I've got a '98 Subaru Outback Sport with an engine swap from an older Legacy (EJ22). it's developed a clicking sound that you only really hear when the engine is under load above ~1500 rpm. If I rev the engine in neutral, you don't really hear the clicking. but if the car is in gear and accelerating (or if I give it a little gas while I'm stepping on the brake), you can hear it pretty clearly.

 

I thought it might be an exhaust leak at first, but it sounds more mechanical. It seems to only be coming from the passenger side, but it'a little hard to tell as I can't really get to the engine while I'm stepping on the brake and gassing it (I know, get a friend to help).

 

Anyway, here are a few videos I've taken where maybe you can hear the sound.

 

1. under the passenger side of the engine while the car is idling. i'm concentrating on the exhaust area. you can sort of hear some clicking, but I'm pretty sure it's normal.

 

2. in the car, revving the engine with my foot on the brake. you can hear the clicking noise.

 

3. revving the engine while in neutral. you can hear some of that clicking right when you start to give it gas and again when the engine winds down.

 

anyone got any ideas what the sound could be?