Help please

[MerlinUK]

For some reason, i herd a hissing noise on my 03 450 ... i checked the usual, rad etc, all seems fine, when i checked the oil via the dipstick, the oil started gushing out, although its definately not over filled.. strange.. Anyone know what it could be? i will drop the oil again tommorrow and refill, but i'm 100% sure it wasnt over filled. Thanks.