318i Timing Chain Rattle
 

I have a 1995 318i , automatic, 127,000 kms. Last few weeks there is a chain rattle noise occuring from engine area, when car idles from cold start. Once car is revved up, the rattle goes away. I am thinking the timing chain tensioner need replacing. Previous posts indicate this is a very easy, and inexpensive job. I have a Bentley manual, and I will be following it when changing the part. But, I was wondering if the timing chain can be observered with cover off, and engine running. Probably NOT !! So, when I remove the cover, and inspect the chain, how will I know if the tensioner needs to be replaced? Should there be ANY slack in the chain? Anything else I should be looking for?
Thanks