I have a Ford Focus 2004 1.6l that has done quite high mileage 155k.
It had a problem wheel bearing on the front right (drivers side) which was replaced along with a full service and some other bits. After this it was silent and driving fine for about 1k miles.
Over the last couple of days it has developed a noise from the rear of the car which appears to be getting louder. It sounds like driving on a flat however I checked the type pressure yesterday and it was fine.
My suspicions is that it is either a wheel bearing on a back wheel or a problem with the exhaust.
The strange thing is that it is loudest from 0-25mph after this it actually gets quieter. Then from 40+mph it seems to come and go but never as loud as it is at around 20mph. This to me doesn't fit with a wheel bearing that tend to get louder and louder with speed from my experience on the front wheel.
How could I try to diagnose this more before getting it to a mechanic?
I really need to narrow it down a bit more to know if its safe to drive as I do around 40 miles round trip a day for work.