If the filter housing is making a buzzing, or fast tapping sound (like when dodgy domestic plumbing makes noises), then there may well be a restriction, or more likely an air-lock in the housing.

Try first bleeding the oil pump housing by loosening the small bolt on the top half a turn or so with the engine running. Make sure oil flows out.

If that doesn't cure it, the take the filter out and replace. You may well have inadvertently let one of the rubber sealing rings slip and/or get trapped between filter and crankcase causing a restriction in flow. Of course if you used a cheap pattern filter, that in itself could be the problem?

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