The first thing you want to do is check the fluid level. If there is a leak and the fluid is low it will cause the slipping when hot. the buzzing noise could be from the lines for the automatic transmission cooler if the fluid is low and is pulsing through the lines or it could be unrelated to the transmission (for example, a loose heat shield on the exhaust).so check the fluid first. if the fluid is low, top it off. I don't know what fluid the rebuilder used but if they didn't use the honda fluid the chances for a seal leak are increased dramatically. if the fluid level is okay, check the color (it should be pink) and smell the fluid (it should smell like oil, and not smell burnt. If the fluid is brown or smells burnt then the chances are its an internal problem.most rebuilders have a warranty on their work. I would strongly recommend you take it back to whoever did the work and have them check it out.hope that helps