Creaking noises from Harman Kardon AVR 7000

I've had a lot of different receivers and amps but the AVR-7000 is the only one that makes noises as it warms up and cools down. The creaking lasts for about 30 minutes until it has reached a stable temp. The unit works perfectly fine except for the creaking which I assume is heat sinks. H/K service didn't have any advice and I hate to send it in for service since it works fine.It's definitely a mechanical noise and not an electronic noise. I've tried different locations and it still creaks. I've had the unit for 2.5 years so the noise isn't going to fade away. It's loud enough that I can hear it almost anywhere in the house.Has anybody else had this problem ? Thanks.
If it really bothers you, I would send it in. You may be missing a screw or other fastener or a weld. I believe the heat sinks are not externally accessible on this unit, and you have to take the cover off to get to them. I would rather send it in before I do that myself. If they're nice, they might fix it for free, since it sounds like a manufacturing defect. Good luck.
It's still under an extended warranty for another 2.5 years. The warranty is supplied by a major canadian electronics retailer and I'm not overly impressed with their repair work. I was just trying to figure out whether it was a common problem with this model. I think I will take it in for service just in case there's a possibility of a short from something not fastened down. Thanks.