09 Forester whistles when accelerating after repair job

Right before Xmas our 09 Forester was hit while parked on the street. The whole front end of our car got wrecked. Was still drivable but we needed a new radiator, ac compressor, fenders, bumper, hood, lights, etc…over 5K worth of work. As soon as we picked it up we noticed that when you press on the gas the car makes a high pitched whistling noise, almost like the noise when you’d try to tune in an old transistor radio. It only happens when the car is driving and the gas is pressed, not when parked or in neutral. I know we should have probably brought it right back to the shop that day but I really did not like the shop at all and they are not at all convenient to where I live. I’ve read it could be a loose cat converter. I checked the air intake housing and that is secure. It’s really starting to drive my wife nuts so any help would be appreciated. Thanks.

First thing I’d be looking at is a vacume leak somewhere. Hose, gasket, etc., cracked, loose, not put back. If you can look under the hood while making it whistle, it’ll be a lot easier to focus on where the noise is coming from.

Yeah the problem is it only makes the noise in gear. I’ve tried a few times to make it happen while in park but it seems to only happen when under load.