Wiscomptonite

Hey guys, novice here. Bought a '97 YZF750 maybe a month ago. Lubbed/adjusted chain and did an oil change. Went from conventional oil to full synthetic mobil 1 15w-50. I'm noticing a buzzing noise coming from the front part of the engine behind the radiator now that I've done the oil change. It makes the noise from start-up all the way through the powerband and is most noticeable at about 4k rpms. Its pretty loud. Any ideas? Was thinking about changing out the oil with a 10w-40 and switching filter brands. Other than this noise the engine runs like an absolute top. All input welcome. Thanks.