I'm finding loose bolts!

[Blue94]

So my car whistles. Okay. I thought it was the o-ring that I replaced on my power steering pump. I replaced it again and it still whistles. Upon closer inspection I found a loose bolt laying on the motor block!! I was alarmed at first but as I reached down for it I noticed that it has been there for a while. I then noticed a hole in the intake manifold where the whistle could have been coming from. Sure enough the bolt went in and the bolt behind it was loose too! That fixed the whistle but my car is falling apart! Is there anything else I should check for just coming apart? Has this happened to anyone else?