Hi, I've got a 2002 wrx bugeye and just recently I've heard this very light knocking noise coming from the ( left hand ) near side of the engine, it's only there at very low revs and when you put ay pressure on the engine, ie, when you pull away and when you change gear and the revs are down around 1000 to 1500, I've recently changed the oil and filter and put mobil 3000 5 w 30 fully synthetic oil in it.
Have I used the wrong oil, OR is this a death rattle.
I understand it's difficult without hearing it, but would appreciate it if someone could tell me what this knocking could possibly be.
Any advice and information is much appreciated.
Thanks In advance.

 

5w30 is too thin.
I'm sure someone will come along and say I'm wrong.
So it's just my opinion.
Could be tappets/lifters
Could be bottom end bearing?

 

Get at least 10w40 fully synthetic in there and see how it goes.

 

What oil was it using before?
I wouldn't be worried too much right now,I know some people do use the thinner 5w30 without problems(the manual does recommend this oil) but you will find most use a thicker oil. 5w40,10w40,10w50 with most common used seems to be 10w40.

Did you do any other work on the car? New plugs?
Could be a loose spark plug?
Or a slight blow on the exhaust.
Hard to diagnose a noise on the tinternet tbh.
I would guess it being a noisy lifter,a slightly heavier oil might quieten this down.
If it is the start of bearing failure then you can drain the oil through a cloth/muslin to see if there are any signs of metal flakes.

Good luck with it and let us know how you get on.