Got a straight 16 trim gun hear air hissing in the top

odd, but may be nose part loose and or the magazine too loose, is your driver bent?
the magazine and the nose part meet check under the cover and make sure all the 3mm hex bolts are secure. should be 4 if im not mistaken.

firstly its always better to change both of the bands even if one is broken this always keeps the drive trim.all seems well clean all the contacts ie battery and gun (do not use any cleaning products this will cause grease)just wipe clean with paper towel.

Here are some easy tests.
Assuming that the gun is firing normally however no nails are ejected. Remove the head of the gun and check if the piston is not returning to top of cylinder (piston needs to return to top for nail to enter into positon under the driver). Piston not returning to top indicates, bent driver or worn oring on piston. Repair /replace as needed. If driver/oring looks good, pull out the cylinder and look for check band in place around series of holes on lower part of cylinder and bumper should not be cracked. Lube all orings with silicone paste lube. Good luck

Push on the button on the rear of the tool to open the magazine. Pull the magazine back. Load nails in the stationary part of the magazine with the heads of the nails at the top of the magazine. Push the sliding section of the magazine back into place making sure it latches.

You have worn or broken o-rings inside the gun. You can take the cap off the gun and check that nothing got pushed into the gun by air pressure that may be stuck in the o-rings, preventing them from holding the air in. Ridgid makes an overhaul kit (part number 079004001084) that contains all of the o-rings needed to rebuild your gun. Use the lube in the kit liberally on the o-rings so they won't get damaged or pushed out of place while you are reassembling the gun.

O rings

Air leaks from the bottom of nailers are due to leaking oring /s that seal cylinder to body of gun and/or leaking thru seal at top of cylinder where headvalve seats. Remove head and examine sealing surfaces of headvalve and top of cylinder. Must be smooth, then pull out cylinder and check oring/s that contact body of gun. Remove any fine scratches on inner body with fine paper (400 grit). Lube with silicone paste. Good Luck!

Try another brand of nails -- maybe your gun doesn't like those. Also, blow any dirt out of the nail magazine.

barrel and fan cover 'o' rings may be leaking/ need replacing. item no 17 on the parts diagram.

Do you have a spark, you should just be able to hear the spark firing when the gun is applied to the work surface and the trigger pulled, it sounds like a click.if no spark heard it could be the switch on the fan head not working , a bad ignitor , or the spark is not sparking in the correct place, chaffed ignition wires.

is the gas you are using in date, there should be a date stamp on the gas bottle. if its out of date it can give problems.

If the air is coming out the trigger it must be replaced. Depending on the model of gun you will have to replace the trigger assembly or various o-Rings. Find a Bostitch dealer in your area and they will supply the parts you require.