pocodon

When I start up my 97 GC the message centre says that there's a rear light malfunction, when I check all the lights they all work, also sometimes when I come to a red light the oil pressure needle drops to nothing and I don't know if it's just my imagination but the engine sounds like a very low, quite thumping sound. A friend thought it was exhaust sounds? I'm wondering if it's engine bearings, anybody have any thoughts on these 2 problems, thanx.