Bathroom faucet gurgling noise?

All I did was change a clogged aerator on my very basic bathroom faucet. Now it makes a gurgling noise for a few seconds after you shut the water off. I tore the trap apart and nothing is clogged. Only thing I noticed was piece going thru floor to main drain pulls right out. (So did my kitchen sink but it didn't matter. I'm not sure but this MIGHT have started a day or 2 after changing the aerator. Reading forums on the net sounds like inadequate venting...but no other drain of any type has an issue. Also it drains fine with absoultely no backup. Thanks in advance!!