Timing Chain?

[fiatosca]

My 101 1300 Giulietta motor is only about 400 miles into its fresh rebuild. It has been smooth a silk since day one. However, yesterday I fired it up and hear a mechanical thrashing from somewhere near the top end. It sounds like it could be a loose timing chain. I stuck my finger into the oil cap and checked the chain tension and it is quite tight, at least between the cams.
Question: Is is possible that the chain tensioer suddenly went belly up? Also,
is it possible for the chain to be under tension between the cams yet slack on the sides? Any other suspects for rattly top end noise? Car seems to run fine otherwise.

[Lo Fo SI]

If the locking nut for the tensioner has come loose then the chain may feel tight when pushed but will thrash around at any speed much above idle. Check the tensioner locking bolt and take the cam cover off and check tension - plenty discussion on other threads about the correct tension.

Simon