Probably a stupid question about my first shotgun

[Onagoth]

Might be the magazine plug.

My mossberg 535 has the same sound and its the mag plug

 

[bandl]

same thing here I just bought a new mossberg 535 today and when i tilt the gun it sounds like a spring or something rattling in the forearm. Can you tell me how to check that Onagoth?

 

[hogiron]

Unscrew the forend, the magazine spring should jump out. Inside the spring should be the wood or plastic plug.

 

[G37]

check the bolt that holds the stock on, my mm had a washer that would slid up and down the bolt when i tilted it back and forth.

bingo!