This motor swap is only a month old and it started knocking yesterday. I've had a motor spin a rod bearing once before so I know what that sounds like. This seems much quieter and is less audible at an RPM that is higher than idle.

I had a shop change the timing belt. They left a bolt loose which cut the timing belt a couple days after I got the car running. Thankfully there was no damage (or so they said), but flash forward a few weeks and I'm hearing this.

Flickr video link below.
http://www.flickr.com/photos/49579200@N07/4785117910/

It sounds like metal to metal contact and I believe it coming from the head, but it's hard to say. If the timing belt were too loose and there was slack, would that cause a similar noise?

 

Ur timing may have jumped a tooth.

 

I just want to know if it's safe to drive. The shop I go to won't be open until Tuesday and I need to drive it to work.

The knocking can't be heard when the car is being driven. Even with the windows down and my head out the window, I can't hear a thing. It's only at idle and it seems to speed up as the RPM rises, but it also get quieter. It can't be heard above 2000 RPM.

 

If it's not getting worse, you can't hear it when you drive, you can't find a ride to work, and you want to chance it, then drive carefully on it