help!! 98 sle bonneville knocking

I have a 98 bonneville sle 3800 i was driving one day had bottomed out a couple of times hard (lots of dips in road) everything was just fine after and even 12 to 15 miles down the road i was turning to get on the highway to come home and about 2 miles further it seemed to drop way off in power could only go 20 to 30 mph tops looked down and temp gauge was pushing towards the red so i pulled it over on the shoulder and popped the hood fans were running and no steam or anything coming from under hood so i shut it off tried to start it back up and it was like a dead battery called a buddy that repo's and he hauled it in for me later i went out to check it out popped the radiator cap it was full and oil was full so i decided to see if it would start it did but there is like a knocking rattling noise coming from the engine almost like the crankshaft is turning in the pan without being attached to the bottom of the engine oil pressure is at 40 psi idling engine has 172,000 miles on it oil changed regularly the knock does quieten down at times and sometimes it cannot be heard at all when it is knocking it is loud i've had rod bearings go out back when i was younger doesn't sound like a rod is it the mains or maybe something else like torque converter what ever it is it made the temp gauge that day go well above normal i'm baffled at this point any help would be appreciated thanks.

Any chance you hit the oil pan against the road when you bottomed out? Get under the car and take a look. Drop the oil pan if necessary.