Broke Valve Spring At Start-up????

[4inastang]

The music has gone sour in my Stang! Just a quick rundown of what's been done over the past couple months:
My car had developed a misfire and was throwing several dtc's. My SCT showed misfires in cylinders 3 and 5. I immediately started pulling the COP's and noticed that the PI intake had cracked underneath the coolant crossover. Coolant had gunked the drivers side head along with the coils and was also running into the valley. A real mess but fixable.
I used my magic search button and decided for the price and my set-up I'd go with the Edelbrock Vic jr and fuel rails. I knew I was going to have a few issues to deal with but with a few good friends at a local machine shop we came up with some 1/2" plate aluminum, cut to size. Sweet! Everything went well other than a misguided fuel fitting. I was really pleased at the looks of the intake and with the procharger and cams, I had some good SOTP pull on the top end of the tach.
Now for the bad news, lend me a shoulder lol. I attempted to crank the car a few days ago and it seemed like the starter was dragging. It would turn over a few times then just give a thud then nothing. I tested the battery and my digital showed 11.5 volts. Being the battery was 04 oem vintage, it was the easy fix. Changing out a starter that's snug against some long tubes is vulgar at best. I hooked up a fresh from the factory NAPA battery today. I re-booted the tune and hit the switch. The engine made no abnormal noises as it turned over but once it fired I could hardly hear a exhaust note over the RATTA TAT TAT TAT.
The idle didn't flutter and the oil pressure was consistent. I only let it run long enough to notice those few things. A couple friends came over that both have had several Stangs and good working knowledge of our cars. Without pulling parts we all came to the assumption that my engine indeed let loose of a valve spring it's ptv clearance virginity had been compromised. I've all but lost my poker face over this.
I know there has to be a few fellow hotrodders here that have gone through this kind of disapointments. I don't know of anything else that could cause this kind of teeth chattering noise. The car isn't being driven or cranked over until this is resolved and I know this one is gonna max out the credit card and no dout my patience.
Gentlemen have any encouraging words other than $#it happens?

 

[trinity_gt]

There aren't often words that can encourage when taps/knocks appear.

Pull the valve cover on the offending side if you suspect a spring. Kind of an unusual thing to go on these engines. Are the springs factory or aftermarket?

Is it possible the engine ingested a screw or bolt? Is the noise definitely coming from the top end (i.e. any chance you're hearing a rod bearing)?

Can you rotate the engine by the crank bolt with a breaker bar to see if you can feel mechanical interference? It's kind of suspicious that the engine hard-stopped with a "thud" while cranking which suggests to me something in a combustion chamber, not necessarily a valve hanging low. If the valve is hanging due to a busted spring the piston should just be able to push it up and out of the way (as opposed to PTV caused by bad timing where the valve is caught between a lobe/follower and the piston...)

 

[4inastang]

Thanks for the reply trinity gt. What you're saying makes good sense. I haven't had a chance yet to pull the cover but we did determine with a stethescope it was coming from the right side. When the thud occurred I had just driven the car a couple blocks to the store and with no symptoms that would worry me. After the thud the engine wouldn't crank so I had it towed. Of course the driver was also a shadetree, "just tap that starter man and she be good". Riiiight lol.
The car has stock valve springs(shakes head, comp beehives setting in the tool box). I hope it's something a bit less costly and complicated to fix. I'm not about to do this in my driveway. Not in this neighborhood. I'll post up more when I pull the pass side cam cover and the plugs. That should give me a much better idea of what happened. I have a few concerned neighboring stang owners that want to know what and how as much as I do. A few of my family members are already parting out my car like I left it to them in a living will.