The problem began when the system ran dry. I added fresh mobile phase solution to the system, primed the pump and finally got some flow going through my RI detector out waste line. I also purge the flow cells, just in case there was a possibilty of air in the cells. Afterwards I noted that my baseline was drifting (descending).
I have tried to determine if the problem is with my Waters 510 pump (note: I had previously changed the seals and cleaned both inlet and outlet chk valves for both pump heads) or the Waters 410 detector. I monitored the baseline w/o flow. Instead of a straight line, I get a noisy baseline. Is there a possibiltiy that there maybe an electrical problem or something else I haven't considered.

If there is air in the cell, you probably won't get it out by pumping mobile phase through it. It would be a good idea to pump 100% MeOH through the cell and then purge the reference side with the MeOH. It will take lots of time to get it to settle back down, so have some patience.

Is Your mobile phase degased? If not, wavy baseline is typical.

We flush the reference channel with 2-propanol during night (low flow) and after that the sample channel at low flow until the baseline is stable. The possibility is that a stable baseline is achieved after 1 or 2 days.

Try to generate some back pressure on outlet tube of detector , when flow( IPA)is on. Use your finger to block the flow and than let is go. This will remove the air from the flow cell.