We have been fighting slide out noise since our trailer was new. All service attempts were lubrication and cleaning, which did not solve the problem. I think Ryan at BAL, finally provided a fix. He suggested loosening the two screws that hold the nylon block on each rail, one half turn looser. Was easy to do with slide partially open. So far, this has solved the problem.
Here is a picture that shows (at least the near side) the plate that puts pressure on the nylon friction plate that rides on top of the slide. The nut on top is welded in place, so loosen the screw below 1/2 turn (per BAL slide manufacturer advice) on two screws on each rail.
I'm having the same problem with my unit. I've had it looked at by my local shop and they did what they did to yours (clean and lube). After moving the slideout a few times since then the squeal is back. Thanks for the recommendation.
BAL says it gives torque specs for these screws (they would not share those with me), but "maybe once a year" the noise situation arrives "due to one of the parts involved being out of tolerance". I'm a retired Mechanical Engineer, the tolerances on the parts involved would be large and could result in large variations (tolerance stack) in the space (or lack of space) between the nylon friction plate and slide arm I don't see where the torque method is worthwhile, seems as each trailer would require its own adjustments.
Sadly the WB service folks only solution is clean and lube, which is only a very brief (if that) solution.
We have not traveled since I loosened the four screws half a turn each, which seemed to solve the noise issue on several slide in/outs. Operation finally 'sounded" very smooth. FINGERS CROSSED that this is a permanent fix!