I have an 07 subaru impreza 2.5i. I've been driving the car for about 1000 miles now and I have a couple issues but no check engine light. The car is bucking/idling rough but when I am driving it's smooth sailing. Also whenever I get over 3k rpm there is a loud continuous screeching noise coming from (what my mechanic thought) was the alternator and the belts. Just installed a new alternator and the noise is still there whenever I go over 3k. The weird part about it all is that there is no check engine light. I had brought it in a while back when I first bought the car to get the check engine light that came on diagnosed, and it was a cylinder misfire. I was teaching myself how to drive the car and was pretty rough on it so ever since the code was cleared it never came back. Any suggestions as to what I might be looking at here?

Thanks!

If the car is making boost when screeching it could be an exhaust leak, most likely from the uppipe, or the turbo is doing something nasty or it could have a boost leak from a hose or gasket, the bucking and idling rough is making me think you have a leak somewhere in the intake tract

THAT IS ASSUMING YOUR CAR HAS A TURBO ??????

forget all that, just googled your car.... No tu-rd blower lol

Have you tried revving the engine with your head in the engine bay to see if you can hear where the noise is coming from?