Engine Rattle at Idle when warm

Hi all,
I've got a rattley engine all of a sudden! I haven't been anywhere bumpy or any thrashed it etc etc, but theres now a notable rattle when the engine is warm. Nothing is obviously loose (thought manifold area) and it only rears its head once warm and at idle/very low revs. It sounds to be coming from the very top of the engine and has got louder over the last 30/40 miles. Oil level is fine, though in the bottom third so doing an oil change tomorrow. Any thoughts? Oh and nearly 118K on the clock
Thanks in advance

Id have a guess at cambelt tensioner if the engine is the g13bb model?

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It is the g13bb model, and googling the same symptoms (albeit on other cars) that seems to turn out to be the case! Damnit

And at low revs, no more than 1500-2000. A fairly knowledgable mate reckons it could be bottom end bearings, going to get to a garage - hopefully local suzuki dealer to get an experienced ear's opinion. How problematic would a partial rebuild be or indeed getting a donor engine and rebuilding that?

Thanks again all!

to do tensioner is easy but do cambelt at same time but if its bottom end bearings its probably worth getting a new engine. but id check tensioner bearing first as its only 35ish for cambelt kit with ensioner bearing included

Thanks Adam, nipping it to the local suzuki dealers a few streets away tomorrow for a trained ear to listen but I'd like to think cambelt idea is plausable as it looks a simple fix!