4440 Front Hydro Pump

I have been deep chiseling the last few days with my 4440 and I noticed a day ago that after it was worked really hard the front hydro pump "grunts" loud for a second when re-starting it after stopping for fuel, etc. It goes away immediately once started and only lasts a second or two on start up. It may have done this occasionally before but not that loud and I never thought much about it. The temp gauge was up near the red all day not in the red just close, definately hasn't been run that hard for years. This is a quad range so just trans pressure light not trans temp. When it was cool the next morning it didn't grunt like that. But I noticed at around 1500 to 1800 rpm the front pump seems to have a whine that wasn't there before and it was still there the next day. Not loud but noticeable. I can't hear it below 1500 and it seems to go away above 1800. Everything is working great though.

1978 model, According to the manual every 1200 hours "have your dealer clean filter in main hydraulic pump". I plan to change the trans filter and clean the intake screen on a rain day, been 600 hours. However what is the main pump filter and is there some trick to it? It probably hasn't been cleaned in forever. Seems strange they would call that out to be done by the dealer. Is it just another screen?

Any ideas on what would cause the "grunt" and 1500 to 1800 rpm whine? Hopefully the filter changes will take care of it. Is this something you guys have encountered?