road noise ???

Morning

not sure if this noise has always been there, and I'm just noticing it suddenly but....

Someone rear-ended my car about 2 weeks ago. I was stationary, so it just needed a new rear bumper. Since then though, I have noticed what seems to be road noise coming from the rear end, but rather than just a constant rumbling noise, it increases in pitch the faster you go. It's particularly loud at 40mph.

Does enveryone's GTA do this ? I'm pretty sure if wasn't like this before.

Any ideas - I've checked the tyres etc. and all look ok - am I worrying about nothing ? Apologies if I'm showing my usual lack of car mechanics knowledge......