Weird rumbling noise after timing belt change?

I just had the timing belt changed on my 2001 Landcruiser, and ever since there is a low rumbling noise, quite noticeable,sort of like the noise a blown bass speaker would make, that seems to come on when the engine hits around 2000 RPMs. Of course the Toyota dealership tells me it can’t have anything to do with their repair, bit does anyone out there have a theory that could explain this? Thanks!

Get another mechanic to inspect the belt and check for proper tension.