My tank smells like salami!

I have a new 35 gallon hexagon tropical tank with a cascade 700 filter,
it come with the hood and light. I leave the light on for about 3 - 4
hours a day. It came with the small pebble stones and a large
decoration/cave(the stones were already cleaned by the pet shop and I
washed off the decoration), it has been set up for about 15 days and a
few days after I filled it, I began to smell this salami smell coming
from the tank. I have checked the Ammonia, Nitrite and pH levels and
all are fine. I change about 5 gallons of the water weekly. I had a
piece of driftwood in it and I have taken that out. I had a rock in
it, I took that out. I have three blue rams, two red honey gouramis,
and four rainbow danios. The pet shop has told me that it is just a
new tank smell and it will go away. But I am beginning to wonder???
Has anyone else had this problem or know what could be causing it? I
drove by our local dump the other day and thought to myself, that it
smelled like my tank (methane gas). Thanks