Errr thanks Arran, sadly I expect it's just use, I didn't check the level since May, the previous owner telling me it didn't use oil between services. Idiot me, then reading the recent engine dying threads here prompted me to check, it was pretty low, a tad under the bottom marker. I wondered why it was tapping a little at the top when idling when hot!! Seems ok now, no unusual noises at all, I WAS worried I might have left it a bit late tho!!