the other week i put a new exhaust gasket on my orion (manifold to downpipe) and yesterday its started making a funny noise.

when the cars stationary or your moving but depress the clutch and rev it, it sounds sweet as a nut but when you pull away or are driving it sounds like its got a really, really bad blowing exhaust.

now obviously its hard to inspect a car thats moving, so im wondering if it might have something to do with the engine moving slightly under load if you know what i mean, and seperating the manifold to downpipe slightly or maybe its something to do with the running gear, but i cant really see how that could be.

any ideas?