I have a trek Excalibur 8 and the gears are changing the selves. Just wondering if anyone else's is having this problem if so what did you do?
I assume this is happening while riding over rough terrain? If so, you will need to upgrade your rear derailleur to one with a clutch type system. Like a Shimano Shadow+ derailleur
Dude. Go to your local bike shop. They are your best source for help. 99% percent of the time when a customer's is ghost shifting, it's because their derailleur hanger is bent. Very easy problem to fix and won't require buying a new derailleur at all.
What Dany said. This is not specific to your bike, it's something that happens to almost all bikes. There are so many variables that could be causing the issue it is hard to diagnose online. Take it to your local bike shop (LBS) and they can get it going for you.
I just had that happen and it turned out the cable housing was separated\broken where you couldn't see it and it was causing the problem. It can also be a stretched cable, derailleur adjustment or bent\loose derailleur hanger.