Limit your water use. Change all the showerheads to low flow and see about installing a field line just for the washing machine. If you have any leaky faucets or toilets they must be repaired.
I had a few customers that added a field line just for their washing machine and their troubles are over. Try letting the system dry out some by not washing clothes at home for a couple weeks.
Always follow the plumbing/health department rules....
Goodluck to you.