Some of you may know that I'm reducing the family VW holding by a quarter and my Passat is getting swapped for a shiny new Merc. He's an early trade-in, going to the dealer on Friday next week and my new ride arrives in September. A mere 29k on the clock at six years old.

For a while I've had a faint rumbling from somewhere at the rear, which I've attributed to saw-tooth wear. It's been quite pronounced on my Golf for a while and this seemed like a mini verison. I also have a teeny, tiny shimmy on the wheel from a slightly out of balance front tyre. So at the weekend I decided to cure both problems and swap the fronts for the rears.

Streuth, what a noise! I would have been certain that I had a front wheel bearing on the way out. I've done a few in my time, including the pressed-in variety and the low speed rumble was a dead ringer. Psychologically, I would have been happier with that than the possibility of an impending DSG box or diff failure. I could have maybe got the offending bearing sorted before trade-in; I certainly wouldn't have wanted to leave it on the car and end up with a big arguement with them.

Anyway, today I started swapping out each tyre for the spare and doing a bit of added fault finding. Nothing cured it until the last swap, completed in pouring rain.

As soon as I took the former offside rear off the front and put it back to its original home the problem disappeared, even with the spare on the front. I put the original front back in its rightful place and still no problem on test drive. Both tyres are Pirelli P Zero with about 6mm of meat, very even wear and no visible problems, no feel of sharp tread on the rear.

I wouldn't have believed the difference a bit of tyre rotation could make and the sense of gloom it inspired when the noise popped up. So chalk this one up to the "remember this" box for next time it sounds like a dodgy front wheel bearing.