I'm back with more of the same. My truck has been in the shop 3 times over the last month - They have replaced the solinoid twice, put all new vac lines and check valves on both wheels, and I still have this problem. My mechanic finally said "Sorry I am out of ideas". When he put the new lines on I drove the truck about 100 miles before the noise came back, so he did something right, it just did not stick.
Anyone here on FTE have any fresh ideas?