I changed to synthetic 3 months ago and then changed the oil filter and oil again every month (so, I've done 3 filter and oil changes in 3 months)because I was afraid the new oil would clean the dirty engine and I actually saw after the first month that the oil was very thick and dirty.

The last time I changed the oil, the used oil was not very thick but was still too dark after just being there for 4 weeks.

My concern is that I started hearing a noise from the engine, when I start it cold in the morning, that disappears after 3 or 4 minutes and doesn't come back until the next morning. It's like spinning a rusty ball bearing without oil, sounds kind of ugly, but then disappears after 3 minutes.

Could that be that the oil is not reaching some specific area in the crankshaft, could the oil pump be clogged?

Is there a suggestion to fix this issue without opening the motor and spending lots of money?

I am using full synthetic 10-30 oil and Mann filters from IPD.usa

it's a 92-960, 6L, 2.9L