A dirty chain will produce chain suck. Also, inspect your granny gear. If the teeth are worn, they may have little burrs on them. These burrs will "hold" the chain and produce the dreded chain suck problem as well.
One solution is to take a link out of your chain. This will add more tension to the rear derailleur spring and will sometimes alleviate the problem. You just have to check and double check that you have enough chain length available to remove a link.
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"Life is not a journey to the grave with the intention of arriving safely in a pretty and well preserved body, but rather to skid in broadside, thoroughly used up, totally worn out, and loudly proclaiming, "WOW, What a Ride!" - unknown
"Your Bike Sucks" - Sky Yaeger