A possible belt problem?

[AW607]

I'm trying to help a good friend of mine figure out an issue with his family's car, an '04 Impreza TS

He tells me there's a loud distinct sound coming from his engine, a sort of humming sound that can sometimes be heard at sometimes idle or during acceleration. He took it for a drive with me and this happened, but I'm not too sure what's up with it. It's been a few weeks since then, and he tells me it got worse.

- because metal vibrates at a certain frequency and if you only hear noise at that particular RPM then something's gotta be lose
- well you heard the humming sound from last time
-this new sound I hear isn't necessarily squealing but sounds like something is slapping against something else
-it's not too loud
-but it happens when my car's idling or when I just start it up and pull out of the driveway

He says a slapping sound so I'm assuming a belt probably's wearing out severely or another similar issue in a roundabout way?

He tells me his father took it to a shop to get it checked out but they said it wasn't an issue and told him not to worry about it.. but since then it just got worse and they didn't bother to help, but he also thinks it might just possibly be a timing belt problem.. Probably does sound quite vague but does anybody have any input on this?

[DiiCii]

take it back or to another shop and ask them to check with a stethoscope. its really hard to determine which noise is which when it comes to being under the hood. stethoscope should help in hearing individual parts