I know exactly what sound you are trying to relay... I heard a ton of those 4.1,4.5 and 4.9's do that back in the day...
The 3800 Tuned Port L27 had problems with the main bearing clearances and in some cases the mains would wear and create too much clearance, seemed to be a problem with the #1 main more so than the others.... The 3300 from 89-93 also suffered this problem.. supposedly GM had corrected the problem but it really seems to be hit or miss.. Some would live to near 200k and other were still prefect at 300k... So you just never know..
Mine on a cold start had a tap until the oil came up to pressure.. But it survived like a trooper.. I still have that original freak year 95 motor and plan on rebuilding it for use in another car..
almost 20 years tho, its been a good van and a good motor.. I can't say anything bad about yours or mine..
and there is that saying, My GM car will run badly longer than your car will run at all...lol