I need some advice on my Chrysler Sebring limited convertible. It's making a weird noise.

I have a 2003 chrysler sebring  conv with a 2.7 engine. It has 87,000 miles
on it. I bought it with 86,000  recently. It"s been making a loud tapping
noise when I start it , the noise doesnt  last but a second or two,but now
when I start it only sometimes do I hear the noise. Also it just started  
making a loud squaling noise when i start it  as well. Noise stops when I
pump the gas quick. I was told by a mechanic that  its the timing chain. The
cost to replace the chain and all that goes with it is 2000. He said the entire
engine had to  come out,and it was a difficult job .   Now the noise is
intermittent ,so  I 'm not sure what to do!!! The car runs great apart from
those two noises!!  What do you think, should I replace the chain, if it is the
chain or wait and see what happens??? Thank You     Tina