First time posting here. I have a 2000 Fat Boy that started making a rattling sound a few days ago. Never really heard that before and the noise would come and go.

Checked oil level and it was fine. Last night riding it home the checking engine light came on and it almost sounds like something broke loose and now sounds like a washing machine.

How bad is the engine screwed up?

 

Pull your cam cover off and check your cam chain tensioners.

 

I had the cam sensor replaced one month ago and now the shop is telling me the sensor is bad again. What would cause this?

 

The cam chain tensioners are the known weak point in the twin cam 88's. they are orange plastic shoes that keep the cam chain tight and have been known to go out at various times on these bikes. As stated above, pull the cam cover and have a look. Also, drain your oil and cut the oil filter open. Look for pieces of orange plastic in it.