Distortion/noise and buzz in front left speaker

No, wd40, "please" first try checking the solder connections, 9 times out of 10 it's bad solder connections. Not every issue with older Electronics is Cap related!!! Onkyo is super easy to repair like I mentioned earlier, check the solder connections first, also check the ribbons, unplug the clean the contacts with DeOxit5, if you still need help, don't hesitate to contact me, good luck!!!

This is likely due to a problem with the amplifier. You may have turned up the amp to the point of overdriving the speaker. The distortion at these high levels cause clipping and turn what was once crisp, clear sound into a muddied, garbled mess.

If the speaker is left connected to that source long enough, damage to the speaker and the amp may occur.

Without changing positions of the speakers: You can disconnect the affect Front or Rear L & R speakers and swap them (connect the L speaker to the R output of the amp and vice-versa). If the buzzing / hum "moves" to the other speaker, then the amplifier has the problem. If the buzzing / hum stays with the same speaker, the speaker has issues and is likely "blown".

Either way, it is probably not going to be a "cheap fix"

Good luck!

Sounds like you have the ground and live possibly the other way around from the head unit to the speakers. The reason for you hearing it from both the tweeter and the speaker is that the tweeter is connected in parallel to the speaker.
Swap the wiring and try it.

Check to be sure that the speaker wires are connected the same for both channels. In other words the phase is the same. If not, then the left is cancelling out the right.

Keep us posted on what you find.

Thanks,
Dan

Have the same amp and speakers, had some trouble getting the imput signals sorted from the HDMI input as im using a PC with HDMI output from the mother board and Windows Media Centre. havent tryed using the mic set up yet.

Did you resolve the issue? have you tried the 7.1 outputs

It might be intereference that's being amplified. Try moving the power pack away from other things. I got the same when it was positioned near a 360 power brick.

I have similar problem with my Onkyo Tx-SR600. It only happens when it's in surround mode. When switch to Stereo or Direct, the scratchiness go away. Still trying to find a solution to this problem.

Disconnect everything from the amp except the power cord, then power on the amp. If the receiver still shuts down, your problem is inside the case and unless you can perform electronic repair yourself you will probably need to take it in for service. If it does not shut down with nothing connected, power it off, connect one speaker or component and power on again. Repeat the process until the amp shuts down and you may have found the bad speaker or other component.

when i connect left front speaker it's shuts down .
That is probably due to protection caused by either
DC or over current. This means your troubleshooting is not complete.
Preform these steps.
Download SR605 service manual.
(a)unplug the amp.
(b)Connect left speaker (c)remove the vertically installed pre-amp board.
See this:
How to do?
1.Unplug the amp.
2.Remove the metal cover.
3.You will see a long vertically installed pre-amp board mounted next to those large power transistors fixed by 12 screws on a large aluminium heat sink.
4.Remove this long vertically installed board mounted by 2 screws.
5.With 2 screws removed, just pulling this board out and hold it with one hand.
(d)Plug the amp and switch it on.
(e)If your amp stays ON forever, the problem is from this long board.
(f)If switch off at once, the problem is from power amp board.
Try the above- mentioned steps to confirm DC or over-
current in left channel.
(g)For DC protection, replace ALL components on left channel of the vertical board.
(h)For over-curremt protection, replace ALL components on left channel.

Replacing ALL components on a faulty channel do not cost you too much.

Could be the result of having DTS compatible equipment connected through the analog inputs on the VSX-409D. Noise and distortion will result as essentially the DTS signal is being played back undecoded. If this is the case you'll have to connect your LD or CD player through the digital connections (coax or optical) and set 'Signal Select' (button on front) to 'Digital'.