Why did dialup modems make noise?

I know that the signal was just tone pulses but why was it when (back in the 90s) when you first connected to the internet you heard a bunch of funny noises. After that if you were to use the internet, it still was using the telephone line, why no funny noises then?

Modems originally allowed you to send data over a network that was designed to only carry voice. Because of that, the communication method between two modems had to be in the audible hearing range (or it would not get carried on the phone line). This is no longer needed because the phone system can now carry both voice and data at the same time (DSL).

The sounds were there all the time, you just needed to pick up the phone to hear it. The reason they played it over a loudspeaker to start with is so you could hear if somthing went wrong with the connection (busy signal, wrong number, a person picked up instead of a modem on the other end, etc).

Because the modem speaker was turned on by default, to give the user the feedback that something was happening during the handshake. With the proper setup of the AT commands you could have 3 modes - always on for speaker, totally silent during operation, and the default with speaker turned on during connect.

They were ATL and ATM if I remember correctly.

But the whole command (Hayes commands) to the modem was:

Attention. Loudness level x.
AT      Lx   (where x is 0 to 3)

Of course this was usually part of a longer string, and many instructions were set by default (unless specifically over-ridden).

Newer modems were able to be set; and stored a default command list.

The whistles and chirps and buzzes that you hear when a modem is going through its initial handshake process is a test of the telephone line quality. A modem send precisely specified sounds and the other listens see what it actually hears on the other end. This way the modems know how clear the line is between them and what sort of frequencies they can use to communicate with each other. The more frequencies they can use and the lower the noise, the higher the speed they'll be able to communicate at.

If a connection ever failed due to connection quality, it would generally fail during this initial handshake process. And if you were listening, you could usually tell why (e.g. you got an answering machine on the other end instead of a modem).

As such, modems were usually configured to play this handshake sequence out loud. This was configured by sending AT M1 to the modem during setup. Alternately, AT M2 means to leave the speaker on all the time, while AT M0 means don't turn the speaker on at all. See the AT command set for more information.

The actual transmission noise that you would hear if you picked up the phone during an active session (as opposed to during this handshake procedure) just sounds like static.

Those noises are the process of the 'hand-shake' going on between your modem and the modem of your ISP. In a literal sense, your modem is calling another modem, much like a classic telephone.

Once the connection is established (after the hand-shake is successful, i.e. the ISP's modem 'picks up'), there is no more need for any 'calling'.