I have a 1998 suzuki sidekick, manual transmission.?

When it's in neutral there's a noise, like something turning and maybe being loose? In gear the noise goes away. It started after I got my master and slave cylinder replaced. I've been through 5 mechanics, one tells me I need a new transmission. Another said it was my throw out bearing, so I replaced the bearing AND clutch. The noise was gone for a day then came back. I know I'm overdue for a trnsmission service. PLEASE HELP! I keep getting different answers from mechanics that just look at it for 5 seconds then quote me 1g or more.