enginew rattle at startup

[Ish]

Hi

When I first start my bike I get a rattling sound that lasts for a few minutes. After that you can't hear it at all. If the bike is left switched for over 15 minutes you will slightly hear the rattle on startup but like I said worst case which is when the bike has been left overnight the rattle lasts for a few minutes.

It doesn't change if I dip the clutch. It sounds like it is from outside the engine rather than inside it.

Any ideas on what it could be?

My bike is a 51 Yamaha Thundercat that has done 24k miles.

 

[Ish]

I've had the noise for a few months.

By outside the engine I meant that the noise seems to be coming from something attached to the engine rather than from inside it but I know sounds can be misleading.

The cam chain tensioner has been suggested.

I also forgot to mention that the noise starts about 5 seconds after my bike has started from cold.

 

[Ish]

I'm going to give the tensioner a try first and will report back.