Modem connection sound, short electronic sound oddity

Question

Hoping someone has an idea about what's happening on my 24" iMac. Leopard 10.5.8, iMac 2.4 GHz Intel Core 2 Duo, Chrome 13.0.782.112.
I've rebooted several times in the past 2 weeks, but the problems described below are still occurring.
About 3 weeks ago, I installed two new Iomega external hard drives - one 2 gb for external storage (firewire) and one 2 gb for Time Machine (USB). I bought the USB drive several months ago, before this model had firewire - just now got around to configuring everything.
A few days later, I noticed what sounded like the dial-up connection sound from a modem - only I don't HAVE a modem. I am connected to Cox cable modem via ethernet. I have heard this sound randomly over the past 2 weeks and it seems to be coming from one of the external drives (I know that sounds nuts, but I turned the sound off on my iMac, trying to troubleshoot). A few days ago, another irritating sound began randomly appearing - kind of a two-note, electronic sound, do-do. Totally random - and this one can be turned off by muting my iMac. It doesn't seem to be happening in response to any specific action. I've observed both behaviors for days now, and can't tie either to anything I'm doing.
The modem sound happens whether I'm using the Mac or not; the little irritating electronic two-tone sound only happens when I'm typing or browsing the Internet. I just this minute thought about the two-tone sound being connected to Chrome or one of the extensions, so I just disabled the 3 extensions but the sound is still happening. I'll try closing Chrome and trying a completely different extension. It's like an alert, but it's not a sound in my alert-sound choices and not the one I have selected.
I prowled through all the system preferences, and all sharing is turned off. The firewall is turned off, with both Firewall logging and Stealth Mode turned on. I switched the firewall setting from "allow essential" to "set access for specific ..." I haven't heard the modem sound again, but that's been happening very randomly and sometimes days apart. At least, when I'm in the room.
The only 3rd-party apps in Preferences are Perian, Flip 4 Mac WMV, and Adobe Version Cue.
No other apps except Chrome are open right now. Bluetooth and Airport are turned off. The little phone handset icon at top right, when clicked, indicates that no modem configurations were found. I checked the firewall log, and mostly see attempted stealth mode connections via TCP or UDP (?) from China, primarily (used whois to backtrack IP addresses). The new attempts don't correlate to the two-tone sound.
Not sure what else to check/try ... hoping someone has an idea. I could have hit a funky key-combo (I type very fast) but the two-tone sound is so random and intermittent, that doesn't seem like it could have caused its sudden appearance. And I am more worried about the modem-connection sound - can that possibly be coming from my Cox cable modem, and/or be an external connection attempt or successful intrusion? My system has never made the sound before - both sounds began appearing when I installed the two new external drives. I "ejected" the external HD that isn't the Time Machine HD, but the two-tone sound is still happening.
Thanks for any assistance!!
Deb

Answer 1

Hi BD - Thanks for the speedy reply, sorry for my own delay (life happened). The "external hard drive logging in" is solved, and you won't believe this - there is a new commercial that features the sound of a dial-up modem connecting to the Internet, and this is what I was hearing. The television and my computer desk are located at the end of a long living room, and I always heard the noise from another room. When I'd come in, the hard drive would be spinning up so all I could assume was that the HD and the noise were related. Geez! It didn't seem at all possible, particularly since I know a HD does not have speakers and I'd muted the Mac, but who would have realized it was a commercial?!?! I was finally sitting at the computer a few days ago, and the commercial came on. Light bulb went on, and the rest is tech-support-funny-story history. No wonder the log activity entries don't correspond to the commercial airing despite the fact that it began airing around the same time I installed the new HDs.
The little two-tone sound was apparently tied to a tab in Chrome - I tried a diff. browser and had no noise, went back to Chrome and it was still there. I began closing tabs and after I'd closed several, I realized the noise was gone. Who knows on that one. No idea why I have the phone handset icon - didn't migrate anything to this machine (still on 10.5.8), but it isn't hurting anything and has always been there. No faxing setup. Actually I need a good website for faxing PDFs - but that's another story. No landline here at home.
Thanks again for your reply and attempt to help me! There is no way, I bet, with ANY amount of troubleshooting that I'd have solved this - glad I didn't waste any more time trying things.
Deb