A common problem on the 2007 Honda Odysseys. Well its a common problem on all Honda V6 engines. Its sounds like a knocking noise is coming from the rear bank cylinder head. Once the tensioner is replaced , the noise goes away. Not very hard to hear. Also, a good way to verify the faulty tensioner is if the noise goes away when the vehicle warms up, the tensioner is faulty. A competent mechanic should be able to do this job relatively fast.
A perennial favorite of ours, the 2007 Honda Odyssey deftly excels at all things important for a minivan. This is one you won't want to miss.