We have a SWAT training going on soon I want to have a couple of fake (but they make a pop sound) trip wire bombs can anyone give me some ideas

Easy.

Party crackers

https://www.amazon.com/s/ref=nb_sb_noss_2?url=search-alias=aps&field-keywords=party&tag=vglnk-c102-20&tag=vglnk-c102-20 crackers&rh=i:aps,k:party crackers&tag=vglnk-c102-20

ETA:  Not sure on the crackers, but these will do the trick, with streamers and confetti.

https://www.amazon.com/PARTY-POPPERS-Birthdays-Weddings-Celebrations/dp/B01K0KUN2O/ref=sr_1_2?ie=UTF8&qid=1481671368&sr=8-2&keywords=party poppers&tag=vglnk-c102-20

Estes model rocket ignitors.  
https://www.amazon.com/Estes-Model-Rocket-Igniters-Pack/dp/B009EZS08G?tag=vglnk-c102-20

Insert into a firecracker of choice.  Rig up a simple switch, and power with a 9V.

If youre doing trip wires just get the air powered airsoft flashbangs. They basically just use a pull pin with a CO2 cartridge to blow up the plastic like a balloon to make it pop.

Just use some old EXPENDED flash bangs or EXPENDED NFDD's.  

SAFETY:  Eye pro, ear pro & face shield.  I like to use aviators gloves as they allow a bit of dexterity while still offering a minimum amount of hand protection.

First, use a punch pin & knock out the spring & striker, then unscrew & remove the fuze portion (bouchon), next use a rod section to knock out the spent primer.  Measure the external diameter of a shotgun 209 primer, and then open up the primer hole on the fuze (its REALLY soft metal) then test fit the 209 primer.  If you made the hole too small, enlarge a bit by either going a hair up in bit size or wobble your drill to open it up.

Use silicon, or elmers glue to hold the primer in place, just a touch around the outside.

Place a POSTIVE BLOCK over your installed primer, and re assemble the spring & striker.  

Cock the striker assembly and pin it.  Then install the spoon.

Keeping ahold of the spoon, compress it down as far as you can without bending your positive block pin holding your striker, then REMOVE the pin (CAREFUL!  As the striker is going to want to force the spoon out of the way & strike the primer!!)

Then repin the spoon & give it a practice go!

Repeat as necessary.

 I have re-done 100's for our training folks.

Will

Depending on ambient temperature, some of these need significant time to build necessary pressure to pop.

These work well.  Look around and you can buy one at a time:  22 cal alarms

These work pretty well IF you modify them by wrapping them with scotch tape as to increase the burst pressure. They are kind of lame in their stock form.

https://www.usfireworks.biz/items/dm-0210-boobytraps.htm