exmark wheel motor going bad?

mowing the other day and i started to hear a slight click / clunk in the right wheel whenever that side stops and goes or changes direction. It does it once (its not multiple clunks in a row) and Sounds like its coming from wheel motor area......don't have any loss of power from that side yet and no leaks. Don't beleive there is any air in the system...am i look at the start of a wheel motor going (machine has 1600 hours)?

thanks for the thoughts on this