A rattle!

[Bcxbcx]

So I heard a rattle today, that has not been there before.

It seems to come from the drivers side of the engine and developed after it was hot (within normal range), it does change slightly with revs (doesn't seem to match revs exactly, maybe a delay) and doesn't go away within the normal, sedate driving rev range.  
It sounds a little like a diesel engine.
Unfortunately I haven't had much time to investigate (and I'm out of time really with work, weddings and birthdays for a couple of weeks to do so in depth, so it might goto a garage).

As a back ground, the car has been great, doesn't seem to use oil; I topped it up when I got it and it has stayed the same level over a thousand or so miles.
The cat heat shield is jubilee clip'd up, to stop that rattle.
I did an oil and filter change at the weekend,  I followed some recommendations on here, after draining, I put 3l in (including pre filling the filter) then topped it up with about 400ml. The dip stick is typically useless, I don't know how anyone reads it with clean oil, it could be full, it could be half full, I could be imagining it and it's just oil smeared from the dip stick tube! (this is what has me worried).
I assume on volume 3.4l plus any remaining oil, would be more than adequate with a 3.7l capacity? I have got those details correct?

A search suggests the diesel sound could be a rattling aux belt tensioner or did I miss understand?

Any ideas or suggestions on what it may be or how to diagnose?

[Carolyn]

A proper fill with filter is 3.7 ltrs.  That allows for residual oil in the engine.  It's slightly under-filled, but not enough to cause a problem.

The rattle may well be a result of giving her clean (and probably different) oil.  It is almost certainly a tired chain tensioner that is not holding pressure too well. Not a difficult job to change it.  They are getting harder to find on the open market, so you might have to get one from Toyota.

It's located on the driver's side end of the cylinder head underneath the spring for the belt tensioner.  There's a 'How to' in the reference section.  There's also one on reading your dip stick.

It could be something in the auxilliary belt train, but the fact that it's appeared after the oil change and is more obvious when up to temperature, makes the chain tensioner the likely suspect and a new one will do no harm.

[Bcxbcx]

Brilliant, thanks for the quick reply.  
I've had a look at the 'how to' for the tensioner and I'll order one in, replace it and go from there.