Same thing here. I have a T61 that's about 9 months old. And about a month ago i started hearing a weird grating/buzzing noise that i first thought was coming from by hard drive. Then realized it was coming from the fan area in the back not the front. And there it is now. Anyways....
I regularly clean my TP out with compressed air and do so in detail when ever i open it, there is usually a dust ball of two every time.You would be surprised how quickly dust can accumulate in computers, Especially when their just sitting on a desk. I thinkl its because of static and magnetic Fields they create. Pulls it right out of the air. And when it dose it can cause shorts or even disrupt ram chips so badly the computer wont recognize them until you've cleaned and reseeded them.
The good news....
Its a simple replacement fix covered under warranty and is not an Uncommon problem (For a Older computer anyways).
I've had a lot of exspirence with computer maitinance and it sounds just like a hard drive going bad. like it has a moter going bad. No amount of cleaning seems to help. The odd Part is occures at weird intervals and not only when the fan is working harder. Im Just waiting for a good time to send it in for service. .
The bad news...
While Im sure this was probubly a bad shipment from toshiba not lenovo's fault. similar problem seem to be occuring with alot of other items on with T6x's Their are alot of T61's with a flaw in the mother board that cause the useport on the right side to be underpowered so that things like usb hard drives and pda chargers .etc.. things that require usb 2.0 to funtion properly. causing problems like the computer not recognizing a device, not charging your pda. or requiering that removable devices be reinstalled everytime it is pluged in. incomplete syinkin of devices. the usb ports on the left are un affected so for most people its not a big deal unless your already using those ports or you plug a wirless mouse reciver in on that side and you right handed.
here is a like for anyone interested
dont get me wrong i love my T61. and i just ordered my second Lenovo thinkpad. but It makes that 3-4 yeat exstended service plan a very good idea.