Recently whilst riding I've been getting the feeling that the rear wheel is 'drifting' slightly to the left as I ride. I've checked that both wheels are secure and aligned correctly, which they are, and have no play in them. The hubs were checked out recently during the bike's last service. The tires are also fine, the tread and sidewalls are in good condition. The frame is also good. I've had a mechanic give the bike a quick look over and there is no obvious problem. I took a fairly heavy spill recently and so have been a bit edgy recently when riding so I could well be imagining it. It's pretty windy and I also have rear panniers. I know this sound a little daft but before I consign it to a sensitive imagination I thought that I'd ask whether there's anything I should check out. Thanks in advance, Paul.