Since purchasing an ’04 Outlander 9 months ago, I have always had a whine from the transmission, starting at about 40mph.
I have changed the oil in the gearbox, 4wd transmission and the rear diff, none have made any difference. I had decided to live with it unless it got worse.

This weekend I decided to fit a set of winter tyres/steel wheels in readiness for any bad weather the UK winter may throw at us. After fitting the new wheels, I took it out for a test drive to make sure everything was OK… Whining noise gone! Totally quiet now, a big difference.

I checked the old tyres that I had removed, and although they had the same size stamped on them, 235/50/18, the front tyres were a different make to the rear and were nearly an inch bigger diameter. This must have been putting a strain on the permanent 4wd system, causing the whine. Hopefully it hasn’t caused any long term damage to the drive system.

BTW. The winter tyres that I have fitted are 215/60/16, which are the correct size for this model. I think the larger 18” type was fitted as a ‘sport’ option.

I was sold on the winter tyres after driving through the snow in Germany last winter where snow tyres are mandatory. I couldn’t believe how much difference they made, especially to the RWD Mercs.